Unusual deuterium isotope effects in 13C NMR spectra of trans‐stilbene

Abstract A detailed analysis of the 13 C NMR spectra of trans ‐stilbene and ten deuteriated trans ‐stilbenes has been undertaken. Some unusual deuterium isotope effects on carbon–hydrogen spin–spin coupling constants could not be explained by the ordinary primary and secondary isotope effects. The positive and negative changes of n J (CH) were interpreted in terms of a steric effect, the vibrational influence of the CD bond and the para ‐effect induced by deuterium. In this respect, deuterium behaves as a real substituent with electronic properties different from those of hydrogen. The deuterium isotope effects on 13 C NMR chemical shifts and carbon–deuterium coupling constants have also been determined.